Standard image sensors have a limited dynamic range of approximately 60 to 70 dB. However, the luminance dynamic range of the real world is much larger. Natural scenes often span a range of 90 dB and over. In order to capture the highlights and shadows simultaneously, high dynamic range (“HDR”) technologies have been used in image sensors to increase the captured dynamic range. The most common techniques to increase dynamic range is to merge multiple exposures captured with standard (low dynamic range) image sensors into a single linear HDR image, which has much larger dynamic range than a single exposure image.
One of the most common HDR sensor solutions would be having multiple exposures into one single image sensor. With different exposure integration times or different sensitivities (for example by inserting neutral density filters), one image sensor could have 2, 3, 4 or even more different exposures in a single image sensor. Multiple exposure images are available in a single shot using this HDR image sensor. However, overall image resolution is decreased using this HDR sensor compared to a normal full resolution image sensor. For example, for an HDR sensor that combines 4 different exposures in one image sensor, each HDR image would be only a quarter resolution of the full resolution image. Hence, improved HDR imaging technologies including new pixel and readout architectures and techniques are desirable.